Cancer of the prostate is the second most lethal cancer in American men, primarily affecting individuals over the age of 50. The number of men at risk for this disease is growing rapidly as the population ages. This research is intended to introduce and evaluate Passive Microwave Radiometry (PMR) technology for the treatment of prostate Cancer. The PMR technique provides noninvasive, passive sensing of temperatures deep within tissue; this allows temperatures within the prostate to be measured using transurethral or transrectal microwave antennas. A major advantage of the PMR system is that temperatures are measured directly from the tissue, eliminating catheter effects. Another advantage is that the same microwave antenna can be used to both deliver hyperthermia and measure temperature. This dual function eliminates the need for additional thermometry catheters. The Phase I Program will seek to determine optimize and characterize temperature distribution of antennas to be developed as an intracavitary hyperthermia system for treating prostate cancer. Combining the PMR system with newly designed transrectal and transurethral applicators should allow intracavitary prostate hyperthermia treatments to be delivered without the need for additional invasive thermometry.